LETTERS ON SCIENCE. I. GEOLOGICAL. [From "The Reader," November 12, 1864.] THE CONFORMATION OF THE ALPS. DENMARK HILL, 10th November, 1864. My attention has but now been directed to the letters in your October numbers on the subject of the forms of the Alps. I have, perhaps, some claim to be heard on this question, having spent, out of a somewhat busy life, eleven summers and two winters (the winter work being especially useful, owing to the definition of inaccessible ledges of strata by newfallen snow) in researches among the Alps, directed solely to the questions of their external form and its mechanical causes; while I left to other geologists the more disputable and difficult problems of relative ages of beds. I say "more disputable" because, however complex the phases of mechanical action, its general nature admits, among the Alps, of no question. The forms of the Alps are quite visibly owing to the action (how gradual or prolonged cannot yet be determined) of elevatory, contractile, and expansive forces, followed by that of currents of water at various temperatures, and of prolonged disintegration-ice having had small share in modifying even the higher ridges, and none in causing or forming the valleys. 1 The Reader of October 15 contained an article "On the Conformation of the Alps," to which in the following issue of the journal (October 22) Sir Roderick Murchison replied in a letter dated "Torquay, 16th October," and entitled "On the Excavation of Lake-Basins in solid rocks by Glaciers," the possibility of which he altogether denied. The reason of the extreme difficulty in tracing the combination of these several operative causes in any given instance, is that the effective and destructive drainage by no means follows the leading fissures, but tells fearfully on the softer rocks, sweeping away inconceivable volumes of these, while fissures or faults in the harder rocks of quite primal structural importance may be little deepened or widened, often even unindicated, by subsequent aqueous action. I have, however, described at some length the commonest structural and sculptural phenomena in the fourth volume of "Modern Painters,” and I gave a general sketch of the subject last year in my lecture' at the Royal Institution (fully reported in the Journal de Genève of 2d September, 1863), but I have not yet thrown together the mass of material in my possession, because our leading chemists are only now on the point of obtaining some data for the analysis of the most important of all forces that of the consolidation and crystallization of the metamorphic rocks, causing them to alter their bulk and exercise irresistible and irregular pressures on neighboring or incumbent beds. But, even on existing data, the idea of the excavation of valleys by ice has become one of quite ludicrous untenableness. At this moment, the principal glacier in Chamouni pours itself down a slope of twenty degrees or more over a rock two thousand feet in vertical height; and just at the bottom of this ice-cataract, where a water-cataract of equal power would have excavated an almost fathomless pool, the ice simply accumulates a heap of stones, on the top of which it rests. The lakes of any hill country lie in what are the isolated lowest (as its summits are the isolated highest) portions of its broken surface, and ice no more engraves the one than it builds the other. But how these hollows were indeed first 1 "On the Forms of the Stratified Alps of Savoy," delivered on June 5, 1863. The subject was treated under three heads. 1. The material of the Savoy Alps. 2. The mode of their formation. 3. The mode of their subsequent sculpture. (See the report of the lecture in the Proceedings of the Royal Institution, 1863, vol., iv., p. 142. It was also printed by the Institution in a separate form, p. 4.) dug, we know as yet no more than how the Atlantic was dug; and the hasty expression by geologists of their fancies in such matters cannot be too much deprecated, because it deprives their science of the respect really due to it in the minds of a large portion of the public, who know, and can know, nothing of its established principles, while they can easily detect its speculative vanity. There is plenty of work for us all to do, without losing time in speculation; and when we have got good sections across the entire chain of the Alps, at intervals of twenty miles apart, from Nice to Innspruch, and exhaust ive maps and sections of the lake-basins of Lucerne, Annecy, Como, and Garda, we shall have won the leisure, and may assume the right, to try our wits on the formative question. J. RUSKIN.' [From "The Reader," November 26, 1864.] CONCERNING GLACIERS. DENMARK HILL, November 21. I AM obliged to your Scottish correspondent for the courtesy with which he expresses himself towards me; and, as his letter refers to several points still (to my no little surprise) in dispute among geologists, you will perhaps allow me to оссиру, in reply, somewhat more of your valuable space than I had intended to ask for. I say "to my no little surprise," because the great principles of glacial action have been so clearly stated by their discoverer, Forbes, and its minor phenomena (though in an envious temper, which, by its bitterness, as a pillar of salt, has become the sorrowful monument of the discovery it 66 1 In reply to this letter, the Reader of November 19, 1864, published one from a Scottish correspondent, signed "Tain Caimbeul," the writer of which declared that, whilst he looked on Mr. Ruskin as a thoroughly reliable guide in all that relates to the external aspects of the Alps," he could not "accept his leadership in questions of political economy or the mechanics of glacier motion." denies) so carefully described by Agassiz, that I never thought there would be occasion for much talk on the subject henceforward. As much as seems now necessary to be said I will say as briefly as I can. What a river carries fast at the bottom of it, a glacier carries slowly at the top of it. This is the main distinction between their agencies. A piece of rock which, falling into a strong torrent, would be perhaps swept down half a mile in twenty minutes, delivering blows on the rocks at the bottom audible like distant heavy cannon,* and at last dashed into fragments, which in a little while will be rounded pebbles (having done enough damage to everything it has touched in its course) this same rock, I say, falling on a glacier, lies on the top of it, and is thereon carried down, if at fullest speed, at the rate of three yards in a week, doing usually damage to nothing at all. That is the primal difference between the work of water and ice; these further differences, however, follow from this first one. Though a glacier never rolls its moraine into pebbles, as a torrent does its shingle, it torments and teases the said moraine very sufficiently, and without intermission. It is always moving it on, and melting from under it, and one stone is always toppling, or tilting, or sliding over another, and one company of stones crashing over another, with staggering shift of heap behind. Now, leaving out of all account the pulverulent effect of original precipitation to glacier level from two or three thousand feet above, let the reader imagine a mass of sharp granite road-metal and paving stones, mixed up with boulders of any size he can think of, and with wreck of softer rocks (micaceous schists in quantities, usually), the whole, say, half a quarter of a mile wide, and of variable thickness, from * Even in lower Apennine, "Dat sonitum saxis, et torto vertice torrens. 1 See below, Forbes: his real greatness, pp. 182 seqq., and the references given in the notes there. 2 Virgil, Æneid, vii. 567. mere skin-deep mock-moraine on mounds of unsuspected ice -treacherous, shadow-begotten-to a railroad embankment, passenger-embankment, one eternal collapse of unconditional ruin, rotten to its heart with frost and thaw (in regions on the edge of each), and withering sun and waste of oozing ice; fancy all this heaved and shovelled, slowly, by a gang of a thousand Irish laborers, twenty miles downhill. You will conjecture there may be some dust developed on the way?— some at the hill bottom? Yet thus you will have but a dim idea of the daily and final results of the movements of glacier moraines-beautiful result in granite and slate dust, delivered by the torrent at last in banks of black and white slime, recovering itself, far away, into fruitful fields, and level floor for human life. Now all this is utterly independent of any action whatsoever by the ice on its sustaining rocks. It has an action on these indeed; but of this limited nature as compared with that of water. A stone at the bottom of a stream, or deep-sea current, necessarily and always presses on the bottom with the weight of the column of water above it-plus the excess of its own weight above that of a bulk of water equal to its own; but a stone under a glacier may be hitched or suspended in the ice itself for long spaces, not touching bottom at all. When dropped at last, the weight of ice may not come upon it for years, for that weight is only carried on certain spaces of the rock bed; and in those very spaces the utmost a stone can do is to press on the bottom with the force necessary to drive the given stone into ice of a given density (usually porous) and, with this maximum pressure, to move at the maximum rate of about a third of an inch in a quarter of an hour! Try to saw a piece of marble through (with edge of iron, not of soppy ice, for saw, and with sharp flint sand for felspar slime), and move your saw at the rate of an inch in threequarters of an hour, and see what lively and progressive work you will make of it! I say "a piece of marble;" but your permanent glacierbottom is rarely so soft-for a glacier, though it acts slowly by friction, can act vigorously by dead-weight on a soft rock, and |